164 



KNOWLEDGE 



[July 1, 1897. 



I have perhaps written sufficient to give an idea of the 

 totally different character of the predominant forest trees 

 of Australia from that of the forest trees of the northern 

 hemisphere. I had almost forgotten to mention the 

 extraordinary size of the trunks of some of these giants. 

 I find many records of trunks between twenty and thirty 



Fig. 8.- 



-A Seed-ressel of Enciliiptus teiraptera. 

 Original drawing. 



ral 



feet in gbth at five feet from the ground, and Mueller 

 mentions a buttressed tree of the jarrah which measured 

 sixty feet in circumference at six feet from the ground. I 

 may add, too, that a cubic foot of green jarrah wood 

 weighs about seventy-five pounds, and, when dry, about 

 sixty pounds. If properly seasoned it is impervious to the 

 marine teredo and the terrestrial white ant, which few 

 other woods can resist. 



With regard to the leaves of gum trees, there are some 

 singular deviations from the typical form described above. 

 Thus, in one species they are sometimes as much as six 

 or eight inches broad, and proportionately long ; in 

 another, the opposite leaves are combined at the base and 

 encircle the branches like the upper ones of the common 

 honeysuckle ; whilst in E. pekatd the stalk is attached 

 above the base of the blade, as in the nasturtium. 



My next article will be devoted to the Proteocia, a family 

 of plants having by far its greatest concentration in 

 Australia, and presenting such an extraordinary diversity 

 in external form (associated with essentially the same kind 

 of floral structiure) as to have suggested its botanical 

 designation. 



♦ 



[The Editors do not hold themselves responsible for the opinions or 

 statements of correspondents.] 



STAR SYSTEMS. 

 To tlie Editors of Knowledge. 



Sirs, — Mr. Monck, in your May issue, page 117, states 

 that when he said the proper motions were not exceptional 



in the case of the five stars, /3, y, 8, e, and I Ursaj Majoris, 

 he was referring to the tjuantity : but may I point out that, 

 in considering what stars belong to a system, the question 

 of the dinction of the proper motion is just as important 

 as any other '? I do not see how anyone can examine the 

 map at the end of Proctor's " Universe " without con- 

 cluding that the proper motions of these five stars are 

 very remarkable, and the figures furnished by Mr. Monck 

 on page 117 do not alter the fact. It is not easy to see from 

 this table the full significance of the figures, and I have 

 therefore had a diagram drawn, where the stars are traced 

 from Proctor's " New Star Atlas." Of course, so con- 

 siderable a portion of the sphere cannot be represented 

 with perfect accuracy on a plane surface, but the diagram 

 is sulficiently near the truth for practical purposes. It 

 differs little from that in Knowledge for November, 1806, 

 page 251 ; but I have added a dotted line to each star to 

 represent the average proper motion of the five ('111 

 seconds of arc in amount), the direction of which is also 

 approximately shown by the long straight line. The 

 following table shows the deviation in each case of the 

 actual from the approximate average proper motion. The 

 second column shows the deviation measured along the 

 line representing the average direction ; the third column 

 that at right angles to this line ; and the fourth a combina- 

 tion of the two, showing the total deviation of the particular 

 proper motion from the average — i.e., it is the distance 

 between the extremities of the two lines for each star, 

 or the amount of the proper motion of the individual 

 star as distinct from that of the system — this individual 

 proper motion including also errors of observation and of 

 measurement of the drawing. 



It will be seen that the motion of none of these stars 

 differs from the average by more than 0-026", which 

 is only about 5 the average of the whole five. Surely, 



iVcale 



when the deviation is so small as this, we must conclude 

 the stars belong to one system. 



Proctor says one may feel absolutely certain that these 

 five stars belong to one system. I take it this is the state- 

 ment to which Mr. Monck objects. It may be that it is 

 an exaggeration of the facts ; but, if so, surely it is a very 

 slight one. Caimot we at least safely say that the majority 

 of these five stars belong to a single system ? It is con- 

 ceivable that a star might by chance have nearly the same 

 proper motion as its neighbour ; but can we believe that 

 this could be the case with five stars in such near agree- 

 ment ? However overwhelming the idea of so vast a 

 system may be, there is no possible escape from it, 

 no matter what assumptions we may make as to the 

 distance of the stars from us. 



Of course there is the question : What do we mean by a 

 system '? Perhaps there may be a difference of opinion on 



